What do you mean with "BIG"???
The belt can be adjusted removing the metal clasps and fitting them in their new position placing it around the figure´s waist and marking it to see where will be the buckle. Place the clasp, clamp it snugly and voila! it´s done.
I you mean "BIG" that the belt is too wide, then it´s nothing to do about it.
I guess you meant the first choice, right?